Lateral cephalograms (full-head x-rays, side view x-rays) are a well-known primary orthodontic analysis tool. Frontal view x-rays have been used to a lesser extent, in part because radiation dosage levels are several times higher and only twenty to thirty percent more information is obtained. Traditionally, a tracing is made of the lateral cephalogram (herein referred to as a "cephalometric tracing") and specific skeletal, dental and soft tissue measurements are then calculated from the tracing. The usual procedure is as follows:
First, a piece of standard tracing paper is fixed to the x-ray film. Next, outlines of key anatomical features are traced with a lead pencil. Then, various lines are drawn by connecting the anatomical landmarks with the aid of a straight edge. The particular lines depend upon the particular analysis or treatment of the patient which has been selected by the orthodontist. The distances between landmarks and angles between pairs of lines are calculated using a ruler and protractor. This information, called "cephalometrics", is used to described the patient's condition in an objective manner which can be communicated with others and used in research, education or diagnosis. If used for diagnosis, the values of these measurements can be the basis for determination of a specific treatment plan for a patient.
The location of certain "landmarks" within the facial complex is the primary information from which cephalometric analysis is made. The preparation of the tracing and identification of the precise location of the landmark teeth involve a certain amount of estimating and the process is far from being an exact science. A complete cephalometric analysis typically requires approximately one hour. Orthodontic schools have been teaching this general method of diagnosis and treatment for decades.
Although there are several variations of general cephalometric analysis, most rely on similar sets of measurements. For example, certain numerical values indicate whether or not to use head gear in treatment. Other measurements suggest a style of head gear to be used. Still others aid in elastic (rubber band) selection. Specific values indicate the magnitude and direction of incisor or molar movement required.
During orthodontic treatment of a patient, a number of cephalometric x-rays may be taken and tracings made in order to monitor the patient's progress toward the desired treatment goal. Additional cephalograms are taken at the end of treatment, and several years after completion of treatment, to determine the level of treatment success. In recent years, there has been reluctance to take such a number of x-rays as a result of concern over radiation exposure. Consequently, more recently orthodontists have not had access to valuable information which could facilitate and improve diagnosis and treatment.
There are a number of cephalometric analysis systems currently in use. The Downs Analysis is described in Downs, W. B., Variation in facial relationships: Their Significance In Treatment and Prognosis, 34 American Journal of Orthodontics, 812-840 (1948). The Steiner Analysis is described in Steiner, C. C., Cephalometrics For Your And Me, 39 American Journal of Orthodontics, 729-755 (1953). The Ricketts Analysis, both frontal and lateral, is described in Ricketts, et al., Orthodontics Diagnosis And Planning, published by Rocky Mountain Orthodontics of Denver, Co. in 1982. The McNamara Analysis is described in McNamara, J. A., A Method of Cephalometric Evaluations, 86 American Journal Of Orthodontics, 449-468 (1984). The Vari-Simplex Analysis is described in Alexander, R. G., The Vari-Simplex Discipline, published by Ormco Corporation of Glendora, Calif. in 1987.
There are certain main categories of data which are used in most cephalometric systems. The first is a patient classification by facial type. Patients with short, wide faces generally respond differently to specific types of treatments than patients with long, narrow faces. Positional data utilizing several external and accessible internal landmarks can be used to adequately categorize any patient by facial type. Relation of the upper jaw (maxilla) to lower jaw (mandible) is determined and is used by the orthodontist to determine if stimulation or inhibition of mandibular or maxillary growth is required to achieve a balanced profile The degree of incisor protrusion, angle of inclination, and the interrelations between upper and lower incisors can be found using a system which generates positional data. This information allows the orthodontist to reposition the teeth in harmony with both jaws, with each other, and with the soft tissue profile (nose, lips and chin).
The use of a computer to generate a cephalometric tracing is known in the art. For example the Ricketts et al. publication referred to above shows, in FIG. 165, a computer generated lateral cephalometric tracing. However, the tracing shown therein was derived from a secondary source of dimensional data, i.e., an x-ray. Consequently, the dimensional information is inaccurate for reasons inherent in the use of x-ray procedures as the source of dimensional data, such as non-linear distortion, as well as requiring that the patient be subjected to x-ray radiation in order to obtain the data.